This invention relates to an apparatus and method to electrostatically charge or neutralize particles conveyed in a pneumatic system. More particularly, the apparatus divides a single gas stream into a multiple several divided streams and charging and polarizing the particles with a high intensity corona discharge. This results in either neutralizing or charging particles with either similar or dissimilar polarities. These particles can be attracted and coalesced into larger particles or separated by repulsion as the particles exit the chambers. Streams with a dissimilar polarity cause the coalescing by attraction as the particles exit the charging chambers.
The pneumatic conveying of powders is used extensively throughout the processing industry. Most of the efforts are spent on neutralizing the charge on particles in order prevent the powders from forming hard clusters and agglomerates that interfere with the flow or cause plugging. In other more serious situations, the accumulation of excessive charges can result in the release of destructive energies.
U.S. Pat. No. 6,017,381 to present inventor shows a cyclone apparatus. With this apparatus there became a need to improve the collection and separation of fine particles. This can be resolved by controlling the charge on the particles entering the cyclone thereby improving the collection efficiency. Particles entering the cyclone are normally triboelectrically charged to varying intensities and with varying polarities. The varying charge conditions can result from either previous or existing process or operating parameters. Another way to vary the charging conditions is through there being differences between the electrical properties of the powder and the construction materials. These variables result in an uncontrolled process with unpredictable collection efficiencies.
In addition, it was found that it is necessary to have the plate and charging electrodes in close proximity to each other in order to improve the ability of ions to follow the flux lines and attach themselves to the entrained particles. Large distances between electrodes and the variation of the particles concentration in the entrained flow can result in the reduced probability of ion to particle attachment. This requires more exposure time to achieve a full charge and larger equipment. Efforts made to understand and control this pre-charging process resulted in the present invention.
The method and apparatus of the present invention electrically charges aerosol and solid particles in a gas stream by dividing and separating a single pneumatic gas/solid stream into two or more streams. The stream is directed into a multiple number of parallel charging sections and exiting back into a single stream. Three electrical states are possible, neutral, attraction, and repulsion.
Particles leaving the multiple charging sections flow into additional processing chambers where the particles can coalesce or be neutralized. Coalescing or the agglomeration of particles takes place when opposing chambers are at different polarity and particles emerge from the respective chambers and inter-react. This can lead to small particles reacting with each other to form larger particles or small particles attaching to large particles to form even larger particles.
Neutralization of particles occurs by using AC corona emission in each chamber. The purpose of neutralizing particles is to prevent clumping or the formation of large clusters of powder that interfere with the flow of materials in a process or pneumatic conveying system. Neutralization can occur in the process of coalescing powders when most of the particles reach a neutral state after they combine, providing the ratio of charge state for the particles are equal.
Repulsion is used to prevent the formation of clusters or larger particles. It is achieved when all of the particles exit the chambers having the same polarity.
The above technology has been used to improve the efficiency of a cyclone to collect fine particles by coalescing the particles before they enter a cyclone. It has also improved the operation efficiency of an electrical cyclone to either collect or separate dissimilar materials. This same technology could be used to improve the operation efficiency of an electrical precipitator to collect fine particles by coalescing particles prior entering a standard precipitator.
When neutralization is the primary requirement or a multi tube is desired, a single conduit composed of an outer dielectric cylinder with charging electrodes and a inner concentric cylinder electrode can be used. Both the multi chamber and concentric tube designs use the same basic technology.